Thin film transparent coatings for modulating optically active materials are currently available for providing "smart" windows whereby the reflective and transmissive properties of the windows can be varied by controlling the transport of electrons and ions into and out of the optically variable layer. U.S. patent application Ser. No. 642,956, filed Aug. 21, 1984 and entitled "Light Modulating Device" describes materials used to form such coatings.
Thin film materials are also known for providing electrical storage batteries having large areas for storing electric energy. The use of specific thin film electro-optically active materials for a solid state battery is described, for example, in a publication entitled "Electrochromic `Smart` Windows" by Ronald B. Goldner, which appeared in the IEEE Reflector Publication, Vol. 35, May, 1987.
For purposes of this disclosure, a thin film electro-optical device has a thickness in the order of several thousand Angstroms in contrast with so-called "thick film" solid state electronic circuits which are in excess of several microns. The aforementioned U.S. Patent Application, which is incorporated herein for purposes of reference, teaches a five layer device deposited on glass for controlling the reflective properties of one of the layers to selectively transmit optical energy through a transparent substrate. Although such thin film devices have been known for some time, commercial utilization of such thin film electro-optic devices has not heretofore been made economically feasible.
One of the modulating layers, the ion-conducting layer, that is used to transport ions into the electrochromic layer must exhibit and maintain two electrically opposing properties. The ion-conducting layer must readily transmit ions upon application of an electric field yet remain electrically insulative to electron transport. Such electrically insulative properties are found to vary over wide ranges of climatic conditions. Materials currently used to form the ion-conducting layer in electrochromic devices are slightly hydroscopic as well as water soluble. Increased moisture content in the air surrounding the electrochromic devices, besides causing variations in the insulative properties, can actually dissolve and hence destroy the coating unless the device is placed in a humidity controlled environment. The mechanical properties of such materials have been found to vary with increasing temperature. For temperatures in excess of 100.degree. C., these materials tend to crystallize, crack and thereby lose adherence to their immediate substrate.
For architectural applications as well as for use within the automotive, aircraft and military applications, rigid performance specifications are required with respect to mechanical strength, resistance to humidity and temperature stability. Temperature specifications for most commercial applications require good mechanical strength at temperatures in excess of 200.degree. C., for example.
One purpose of this invention therefore is to describe methods and materials for providing an electrically active layer having good ionic transport properties along with high electronic resistance, while retaining high physical integrity over wide ranges of temperature and humidity.